Electronic toll collection systems conduct toll transactions electronically using RF communications between a vehicle-mounted transponder (a “tag”) and a stationary toll plaza transceiver (a “reader”). An example of an electronic toll collection system is described in U.S. Pat. No. 6,661,352 issued Dec. 9, 2003 to Tiernay et al., and owned in common with the present application. The contents of U.S. Pat. No. 6,661,352 are hereby incorporated by reference.
In a typical electronic toll collection (ETC) system, a set of antennas are disposed to cover the roadway with overlapping coverage zones. Each antenna broadcasts a wakeup or trigger RF signal within its coverage zone. A tag on a vehicle passing through the coverage area or zone detects the wakeup or trigger signal and responds with its own RF signal. The tag responds by sending a response signal containing information stored in memory in the transponder, such as the transponder ID number. The response signal is received by the antenna.
The antennas operate under the control of a reader that typically uses time multiplexing to scan the roadway for transponders using each antenna in turn. When an antenna receives a response signal, the response signal is input to the reader, which may then conduct an electronic toll transaction, such as by debiting a user account associated with the transponder ID number. The reader may then cause the antenna to broadcast a programming RF signal to the tag. The programming signal provides the tag with updated information for storage in its memory. It may, for example, provide the tag with a new account balance.
In one electronic toll collection system, the reader may include a single RF transceiver, a multiplexer, and a controller. The controller controls operation of the RF transceiver and conducts the toll transactions. The controller may cause the multiplexer to selectively connect the RF transceiver to each of the antennas in turn, thereby implementing time multiplexed scanning. It will be appreciated that failure of the RF transceiver results in a total loss of coverage.
In another electronic toll collection system, the reader may include an RF transceiver for each antenna. In this case, a failure of an RF transceiver causes a loss of coverage corresponding to the coverage area of the antenna connected to the failed transceiver. This may mean that a lane within the roadway has no effective coverage. This loss of coverage may be difficult to detect, since the majority of the system remains operational. Accordingly, the defect may persist for days without discovery. This is especially so in cases where there is overlapping coverage, such as where a lane is partly served by a center-lane antenna and mid-lane antennas on either side.
It would be advantageous to have an improved electronic toll collection system.